Many institutions, such as banks and airlines, allow customers and other callers to access over the telephone a wide variety of services and account information. Before the advent of touch-tone telephones, a caller would obtain these services and information through interacting with a live operator. As touch-tone telephones became more prevalent in homes, these institutions began switching to automated caller-access systems. After dialing a telephone number, a caller using such systems would be asked to enter an identifier or confirmation number. An identifier typically comprises a string of alphanumeric characters.
When using touch-tone phones with an automated caller-access system, a caller can enter an identifier by sequentially pressing a series of keys provided on the telephone keypad. Each pressed key corresponds to a different character in the identifier. The pressing of these keys produces a series of tones that are provided over a telephone network to the institution. At the institution, the series of tones are decoded to produce the entered identifier, and if the identifier entered by the caller is determined to correspond to a valid identifier, then the caller is allowed to enter commands, again through the telephone keypad, that provide access to whatever services are offered by the institution.
Recently, automated caller-access systems have eliminated the use of telephone keypads to obtain the identity of a valid caller. Instead of entering an identifier through a telephone keypad, a caller is prompted to speak the identifier into the telephone handset. For example, the caller may speak into the telephone the identifier "JB123E". The caller's voice signal is transmitted over the phone lines to the institution, which employs a speech recognition system to produce a recognized identifier that is intended to correspond exactly to the identifier spoken by the caller.
However, such exact correspondence is difficult to attain due to, for example, the deterioration of voice signals that routinely occurs over conventional telephone lines, and the different ways the same words are pronounced by different users. Because of these problems, the speech recognizer may confuse similar sounding letters and numbers. Thus, a speech recognizer may confuse the letter "A" with the number "8", the letter "K", or the letter "J". Similarly, the speech recognizer may confuse the letter "C" with the letter "D" or the number "3". For example, given that a caller speaks the identifier "JB123E" into a telephone, the speech recognizer may produce "AE123D" as an output.
In order to compensate for inaccuracies, many speech recognition systems used by businesses must request that a caller pronounce the word multiple times, or be subject to various confirmation routines. This can be time consuming and frustrating to the caller.
Based on the foregoing, there is a need for a speech recognition system that has an increased caller identifier recognition accuracy compared to known speech recognition systems.